The present invention relates to an information recording medium.
Recently, various optical recording and reproducing apparatus using a recording medium such as an optical file and compact disc have been proposed. Also, a card type optical recording medium (hereinafter called optical card) and a method of using the same have been proposed, which is superior in portability and relative memory capacity to those of the above-noted apparatus.
FIG. 1 schematically shows a plan view of a record format of a conventional optical card. In the figure, formed on an optical card 1 used as a recording medium is a recording area 2, which is constituted by a plurality of bands 3. Each band 3 is constructed of a plurality of sets, one set including a track 4, and start bit and stop bit to be described later. The track 4 has an information capacity of about several fens to 100 bits. Each band is partitioned by a reference line (hereinafter called R line). The arrow A indicates the direction of movement of the optical card 1 during reproduction.
FIG. 2 schematically shows the construction of an optical reproducing apparatus. In the figure, the optical card 1 is movable in the direction of the arrow A by means of a rotary mechanism 6. Information recorded on the optical card 1 is read with an optical head 11 and reproduced respectively for each track. In particular, light from a light source 7 such as an LED is focussed by an optical lens system 8 to apply it onto a certain track on which information has been recorded An image from the light-applied track 4 is focussed onto a linear sensor array 10 by an optical focussing system 9, so that an electrical signal corresponding to the information recorded on the track 4 is outputted from the sensor array 10. After completion of the readout of the track 4, the optical card 1 is moved in the direction of the arrow A or the optical head 11 is moved in the direction of juxtaposition of the bands 3 (i.e., in the direction of the arrow C), to further process the next information readout from the track 4.
FIG. 3 schematically shows an enlarged portion of the conventional record format shown in FIG. 1. Hatched portions indicate an information "1". In the figure, on opposite sides of the information track 4, there are formed a start bit 21 indicating the start of the information track 4 and a stop bit 22 indicating the end of the information track. Both bits are opposite to each other in optical characteristic (i.e., if one bit information is "1" then the other is "0"), and are inverted in optical characteristic for each adjacent track. The R line 5 has two bits and is disposed in the form of a stripe across the bands 3. The readout operation of the information track 4 by the sensor array 10 is initiated upon detection of a separating area information "001100" including two bits of the R line 5. At the start of reading of the information track 4 the start bit 21 information is stored, and after the end of reading of the information track 4 the stop bit 22 information is stored. Thus, since both bit informations are inverted for each adjacent track, it is possible to recognize a start of reading of a new information track by the sensor array 10. Such a method for detecting a new information track becomes necessary when one information track is scanned plural times by the sensor array 10 while the scanning of the sensor array 10 and the movement of the optical card are carried out asyhchronously
The conventional record format has some problems. There is quite a possibility that the information track may contain the same information as that of the separating area including the R line information (in this example, "001100"); and the detection of the R line and the discrimination between information tracks are degraded in accuracy.
Further, since the start and stop bits are essential to the conventional record format, if the number of bits within one track is small, the ratio of the number of start and stop bits to the whole number of bits within one band becomes large. Therefore, the information storage capacity is reduced.